The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
4-(3-(4-cyano-3-(trifluoromethyl)phenyl)-5,5-dimethyl-4-oxo-2-thioxoimidazolidin-1-yl)-2-fluoro-N-methylbenzamide (INN name is Enzalutamide; CAS No. [915087-33-1] is an androgen receptor inhibitor for the treatment of castration-resistant prostate cancer, having molecular weight 464.44 g/mol and molecular formula C21H16F4N4O2S, and can be structurally represented as Formula (I).

U.S. Pat. No. 7,709,517 B2 (the U.S. '517 patent) discloses diarylhydantoin compounds, including diarylthiohydantoins, and methods for synthesizing them and using them for the treatment of hormone refractory prostate cancer. Example 56 of the U.S. '517 patent discloses the process for preparation of enzalutamide.
U.S. PG-Pub. No. 2013/190507 A1 (the U.S. '507 A1) discloses process for the preparation of diarylthiohydantoin and diarylhydantoin compounds including enzalutamide. Example-5 of the U.S. '507 A1 discloses enzalutamide as compound of Formula I-1 in 82% yield as white powder with 0.14% moisture by KF and having greater than 99.9% purity by HPLC. Further, example-8 of the U.S. '507 A1 discloses enzalutamide as compound of Formula I-1 obtained by purifying crude material by column chromatography wherein the analytical data were in agreement with that of example-5.
The U.S. '507 A1 discloses process for the preparation of enzalutamide and related compounds. The U.S. '507 A1 discloses the preparation of enzalutamide designated as compound I, 2-I starting from compound A as depicted in scheme-1.

The U.S. '507 A1 also discloses the alternative synthesis of compounds of I or 2-Ia, wherein R7 is —C(═O)OH which is illustrated in scheme-2 below.

The U.S. '507 A1 in example-10 further discloses the process for the preparation of diarylhydantoin of formula M-1 by reacting 4-(1-Carboxy-1-methyl)-ethylamino)-2-flouro-benzoic acid and 4-isothiocyanato-2-triflouromethylethylbenzonitrile in presence of triethylamine in ethanol solvent as depicted in scheme-3.

U.S. PG-Pub. No. 2013/0079372 A1 discloses the process for the preparation of substituted phenylcarbamoyl alkylamino arene compounds and N,N′-bis-arylurea compounds. These compounds are intermediate compounds for the preparation of diarylhydantoin compounds as disclosed below.

International (PCT) Publication No. WO 2014/043208 A1 discloses a pharmaceutical composition comprising a solid dispersion containing enzalutamide and a polymer, wherein the polymer is 0.5 to 7 parts by weight, with respect to 1 part by weight of the enzalutamide.
International (PCT) Publication No. WO 2014/041487 A2 discloses process for the preparation of cyrstalline Form R1 of enzalutamide. Also discloses crystalline form R2 and an amorphous form of enzalutamide and their process for preparation.
Therefore, there is need to provide an alternative process for the preparation of androgen receptor inhibitors like enzalutamide.